Batteries
Internal resistance is a concept that helps model the electrical consequences of the complex chemical reactions inside a battery. It is impossible to directly measure the internal resistance of a battery, but it can be calculated from current and voltage data measured from a circuit. When a load is applied to a battery, the internal resistance can be calculated from the following equations:
or
where
is the internal resistance of the battery
is the battery voltage without a load
is the battery voltage with a load
is the total resistance of the circuit
is the total current supplied by the battery
Internal resistance varies with the age of a battery, but for most commercial batteries the internal resistance is on the order of 1 ohm.
When there is a current through a cell, the measured e.m.f. is lower than when there is no current delivered by the cell. The reason for this is that part of the available energy of the cell is used up to drive charges through the cell. This energy wasted by the so-called "internal resistance" of that cell. This wasted energy shows up as lost voltage. Internal resistance is r = (E−V)/I .
Read more about this topic: Output Impedance
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